1. Field of the Invention
The present invention relates to a coating unit and a coating method for a substrate.
2. Description of the Related Art
In a photolithography process, for example, in semiconductor device fabrication processes, resist coating treatment for applying a resist solution on a surface of a substrate, for example, a semiconductor wafer (hereinafter referred to as a ‘wafer’), to form a resist film, exposure processing for exposing the wafer in a pattern, developing treatment for developing the wafer after being exposed in the pattern, and so on are performed to form a predetermined circuit pattern on the wafer.
The above resist coating treatment is usually performed in a resist coating unit, and for example, a cylindrical cup with an upper part thereof being open is provided inside a casing of the resist coating unit and a spin chuck for holding the wafer by suction to rotate the wafer is provided inside the cup. The resist coating treatment for the wafer is performed in a manner in which the rotated wafer is supplied with the resist solution onto the center thereof, the resist solution on the wafer is diffused by a centrifugal force which is caused by the rotation, and a uniform resist film is formed on the wafer.
Furthermore, atmospheres inside the casing and the cup need to be maintained at predetermined temperature and humidity when the resist coating treatment is performed. For this purpose, a supply device for supplying gas such as air and inert gas to the wafer inside the cup and an exhaust device for exhausting the atmosphere inside the cup from a bottom portion of the cup are provided in the resist coating unit. Conventionally, only this exhaust device is provided as an exhaust device for exhausting an atmosphere inside the resist coating unit and an amount of the gas supplied by the supply device and an amount of the atmosphere exhausted by the exhaust device are adjusted to maintain a processing environment of the resist coating treatment.
However, since film thickness of the resist film varies depending on a flow speed when the above-mentioned gas is supplied, it is necessary to maintain the flow speed of the gas within a predetermined range and it is also necessary to maintain a pressure inside the casing at a positive pressure in order to prevent impurities from the outside of the casing from flowing into the casing while maintaining a flow rate of the above-mentioned exhausted gas at a certain level or higher in order to prevent impurities produced from the wafer from flowing out of the cup. Therefore, it is very difficult to adjust each of the exhaust flow rates and the flow rate of the supplied gas with only one exhaust device and the supply device as described above to satisfy all of the above conditions.